The invention relates to an internal combustion engine for a motor vehicle, and to a method for operating such an internal combustion engine.
Such an internal combustion engine as well as a method for operating such an internal combustion engine, are known from the disclosure of DE 10 2008 064 264 A1. The internal combustion engine includes at least two combustion chambers as well as an exhaust gas tract. The exhaust gas tract has at least one exhaust gas duct, which is associated with the combustion chambers and through which exhaust gas from the combustion chambers can flow, in order to guide the exhaust gas to a turbine of an exhaust gas turbocharger In other words, the at least one exhaust gas duct is or can be connected fluidically to the at least two combustion chambers, so that the exhaust gas flows out of the combustion chambers into the at least one exhaust gas duct and flows through the latter.
Furthermore, an exhaust gas recirculation line is provided which is branched off from the exhaust gas duct. By means of such an exhaust gas recirculation line the exhaust gas is at least partially diverted out of the exhaust gas duct and is recirculated from the exhaust gas tract to an intake tract of the internal combustion engine. The recirculated exhaust gas can flow in with fresh air into the combustion chambers and can act as inert gas in combustion processes running in the combustion chambers. As a result the production of so-called hotspots during the combustion processes occurs. Points at which excessive temperatures occur during combustion are referred to as hotspots. As a result of these high local temperatures, increased production of nitrogen oxides can occur at the hotspots. By means of the exhaust gas recirculation system nitrogen oxide emissions (NOx emissions) can be kept low.
Furthermore, an adjustable shut-off element can be provided by means of which a respective cross-section, through which exhaust gas can flow, of the exhaust gas recirculation line and of the exhaust gas duct can be adjusted. Thus one and the same shut-off element makes it possible to change the cross-section of the exhaust gas recirculation line and of the exhaust gas duct through which exhaust gas can flow. The exhaust gas recirculation rate can for example be set appropriately in a simple and favorable manner by means of the control element.
DE 10 2009 004 418 A1 discloses a method for the after-treatment of an exhaust gas stream of a multi-cylinder internal combustion engine of a vehicle, in particular of a commercial vehicle. The internal combustion engine has a plurality of different groups of cylinders, each having an air supply conduit and an exhaust gas conduit associated with it. The exhaust gas conduits open in multiple ducts into an exhaust gas turbine, designed accordingly with multiple ducts, of an exhaust gas turbocharger, wherein an exhaust gas after-treatment element is connected downstream of the exhaust gas turbine. In a heating mode of the internal combustion engine predetermined in accordance with predetermined operating parameters of the internal combustion engine, in particular in idle or light-load mode of the internal combustion engine, a first part of the cylinder groups formed by at least one heating cylinder group is operated in a fired mode to a predetermined extent, whilst another second part of the cylinder groups formed by at least one shut-down cylinder group is operated in a part-fired mode or in an unfired mode either with a reduced quantity of fuel relative to a defined normal operation and/or relative to a quantity of fuel metered into the at least one heating cylinder group.
An unfired operation of combustion chambers, in particular cylinders, of an internal combustion engine designed for example as a reciprocating internal combustion engine is usually also referred to as cylinder shut-down or as cylinder shut-down mode. Fuel can be saved by such a cylinder shutdown, as usually no fuel is introduced into the combustion chambers which are operated in the unfired mode. However, in the case of such a cylinder shutdown problems may occur with achieving a sufficiently high exhaust gas recirculation rate, that is to say being able to recirculate a sufficiently large quantity of exhaust gas from the exhaust gas tract by means of the exhaust gas recirculation line to the intake tract, in order to be able to keep the production of nitrogen oxides low in the combustion chambers that are still being operated in the fired mode.
It is therefore the object of the present invention to create an internal combustion engine as well as a method for operating such an internal combustion engine by means of which operation of the internal combustion engine can be implemented with particularly low fuel consumption whilst simultaneously achieving sufficiently high exhaust gas recirculation rates.
In order to create an internal combustion engine for a motor vehicle, by means of which operation of the internal combustion engine can be implemented with particularly low fuel consumption whilst simultaneously achieving sufficiently high exhaust gas recirculation rates, it is provided according to the invention that the internal combustion engine can be operated in a cylinder shut-down mode in which introduction of fuel into a first combustion chamber is prevented and introduction of fuel into the second combustion chamber takes place. In other words, in the cylinder shut-down mode the second combustion chamber is supplied with fuel, so that combustion processes run in the second combustion chamber. These combustion processes result in exhaust gas which flows through the exhaust gas duct and can be diverted into the recirculation line which is or can be connected fluidically to the exhaust gas duct.
In the cylinder shut-down mode the first combustion chamber is not supplied with fuel, so that the first combustion chamber is operated in a non-fired or unfired operational state. As a result the fuel consumption of the internal combustion engine can be kept low. However, since exhaust gas from the second cylinder flows through the exhaust gas duct, a particularly large quantity of exhaust gas can be recirculated so that particularly high or sufficient exhaust gas recirculation rates can be achieved. As a result the nitrogen oxide emissions can be kept low.
In this case the exhaust gas recirculation rate is adjustable appropriately by means of the shut-off element, wherein by means of one and the same shut-off element both the cross-section of the exhaust gas duct through which the exhaust gas flows and also the cross-section of the exhaust gas recirculation line through which the exhaust gas flows can be adjusted. In this case, however, every change to the cross-section of the exhaust gas recirculation line through which the exhaust gas can flow is not necessarily accompanied by a change to the cross-section of the exhaust gas duct through which the exhaust gas can flow. However, if the cross-section of the exhaust gas duct through which the exhaust gas can flow is decreased by means of the shut-off element, a particularly simple setting of a particularly high exhaust gas recirculation rate can be achieved in this way.
The cylinder shut-down mode, which is usually also referred to as cylinder shut-down, is preferably set in the partial-load mode of the internal combustion engine, in which a torque of the internal combustion engine required by the driver of the motor vehicle can also be provided when only a part of the combustion chambers thereof is operated in a fired mode and another part of the combustion chambers is operated in an unfired mode, that is to say they are operated in the cylinder shut-down mode.
In an advantageous embodiment of the invention the shut-off element can be shifted between a first position and at least one second position. In the cylinder shut-down mode the shut-off element is shifted into the second position, in which the cross-section of the exhaust gas recirculation line is enlarged relative to the first position and the cross-section of the exhaust gas duct is reduced in size. As a result particularly large quantities of the exhaust gas flowing through the exhaust gas duct are diverted and flow through the exhaust gas recirculation line, so that as a result particularly high exhaust gas recirculation rates are feasible.
It has been shown to be particularly advantageous if the cross-section of the exhaust gas duct is shut off fluidically by means of the shut-off element in the second position. As a result, in the cylinder shut-down mode at least substantially all of the exhaust gas flowing through the exhaust gas duct or flowing into the exhaust gas duct and flowing at least to the exhaust gas recirculation line can be drawn off from the exhaust gas duct and delivered to the exhaust gas recirculation line, in order thus to be able to achieve particularly high exhaust gas recirculation rates in spite of the cylinder shut-down being carried out.
In a particularly advantageous embodiment of the invention it is provided that, by comparison with different positions into which the shut-off element can be shifted, the second position is a position which frees the cross-section of the exhaust gas recirculation line to the maximum extent. In other words the shut-off element can be shifted into a plurality of positions which do not shut off the cross-section of the exhaust gas recirculation line but at least partially free it, also including the second position. In this case the second position is the position in which the cross-section of the exhaust gas recirculation line is freed relative to the other positions which at least partially frees the cross-section of the exhaust gas recirculation line to the utmost, that is to say to the maximum extent. As a result flow resistances for the exhaust gas flowing through the exhaust gas recirculation line can be kept low, so that a particularly large quantity of the exhaust gas can be recirculated in a short time.
In a further advantageous embodiment of the invention the internal combustion engine has at least one third combustion chamber, wherein the exhaust gas tract has at least one second exhaust gas duct which is associated with the third combustion chamber, and through which exhaust gas from the third combustion chamber can flow and which is at least partially separated fluidically from the exhaust gas duct for guiding the exhaust gas to the turbine. In other words, the second exhaust gas duct is or can be connected fluidically to the third combustion chamber, so that the exhaust gas from the third combustion chamber can flow into the second exhaust gas duct and can flow through the latter. In this case it is provided that an introduction of fuel into the third combustion chamber takes place in the cylinder shut-down mode. As a result high outputs or torques can also be provided by the internal combustion engine in the cylinder shut-down mode.
In this case it has been shown to be particularly advantageous if the first exhaust gas duct is associated with a first turbine duct and the second exhaust gas duct is associated with a second turbine duct of the turbine which is at least partially separated fluidically from the first turbine duct. In this case the first turbine duct has a smaller flow cross-section through which the exhaust gas can flow than the second turbine duct. In other words, the first exhaust gas duct serves for guiding the exhaust gas to the first turbine duct. Thus the exhaust gas can flow in from the first exhaust gas duct into the first turbine duct. The second exhaust gas duct serves for guiding the exhaust gas to the second turbine duct, wherein the exhaust gas from the second exhaust gas duct can overflow into the second turbine duct.
In this case the turbine ducts are designed asymmetrically with respect to one another, the first turbine duct being smaller than the second turbine duct. Thus the first turbine duct has a better accumulation characteristic for the exhaust gas than the second turbine duct, so that in this way particularly high exhaust gas recirculation rates are feasible. The cylinder shut-down for reducing the fuel consumption takes place in the first combustion chamber and thus in a combustion chamber associated with the first exhaust gas duct and thus to the first turbine duct, whilst the third combustion chamber associated with the second exhaust gas duct and the second turbine duct is supplied with fuel in the cylinder shut-down mode and consequently is operated in a fired mode.
It is preferably provided that the number of combustion chambers which are associated with the second exhaust gas duct and the second turbine duct, and which are supplied with fuel in the cylinder shut-down mode, is greater than the number of combustion chambers of the internal combustion engine which are associated with the first exhaust gas duct and thus with the first turbine duct, and which are supplied with fuel in the cylinder shut-down mode. All combustion chambers of the internal combustion engine which are associated with the second exhaust gas duct and thus with the second turbine duct are preferably supplied with fuel in the cylinder shut-down mode and consequently are operated in a fired mode. As a result, the second exhaust gas duct and the second turbine duct are used for guiding a predominant part of the entire exhaust gas from the internal combustion engine. Since the second turbine duct is larger than the first turbine duct, flow resistances for the predominant part of the exhaust gas can be kept low, so that a particularly high degree of efficiency of the internal combustion engine is achieved. This is accompanied by operation which is efficient and thus economical in terms of fuel consumption.
Furthermore the smaller, first turbine duct or the first exhaust gas duct corresponding thereto can be used in order to achieve particularly high exhaust gas recirculation rates. The second combustion chamber associated with the first exhaust gas duct is used as a dispenser cylinder from which the exhaust gas is at least partially and preferably completely recirculated.
In order to create a method by means of which operation of the internal combustion engine can be achieved with particularly low fuel consumption and particularly high recirculation rates, it is provided according to the invention that the internal combustion engine is operated in a cylinder shut-down mode in which introduction of fuel into a first combustion chamber is prevented and introduction of fuel into the second combustion chamber takes place. In other words, in the cylinder shut-down mode fuel is introduced into the second combustion chamber, so that this chamber is operated in a fueled or fired operational state in which combustion processes run in the second combustion chamber. These combustion processes result in exhaust gas which can be recirculated by means of the exhaust gas recirculation line to an intake tract of the internal combustion engine.
In the cylinder shut-down mode the first combustion chamber is not supplied with fuel, so that the first combustion chamber is operated in an unfired or non-fired operational state. As a result can fuel savings can be made. Advantageously embodiments of the internal combustion engine according to the invention may be regarded as advantageous embodiments of the method according to the invention and vice versa.
In an advantageous embodiment of the invention the shut-off element can be shifted between a first position and at least one second position, wherein the shut-off element is shifted into the second position in the cylinder shut-down mode, so that the cross-section of the exhaust gas recirculation line is enlarged relative to the first position and the cross-section of the exhaust gas duct is reduced in size. Due to the reduction in size of the cross-section of the exhaust gas duct a backing-up or accumulation characteristic of the exhaust gas duct is set, so that particularly large quantities of exhaust gas can be recirculated. Furthermore, the cross-section of the exhaust gas recirculation line is freed in such a way that the large quantity of the exhaust gas can flow through the exhaust gas recirculation line in a manner which is favorable in terms of flow, so that particularly large quantities of the exhaust gas can be recirculated in a short time.
It has been shown to be particularly advantageous if the cross-section of the exhaust gas duct is shut off fluidically by means of the shut-off element in the second position. As a result, all of the exhaust gas flowing through the exhaust gas duct to the exhaust gas recirculation line can be used and recirculated.
Further advantages, characteristics and details of the invention can be seen from the following description of a preferred exemplary embodiment and with reference to the drawing. The features and combinations of features stated above in the description and the features and combinations of features stated below in the description of the drawing and/or shown in the single drawing can be used not only in the specified combination in each case, but also in other combinations or in isolation without departing from the scope of the invention.